Scientific theories based on mathematical models are frequently used in sciences to reveal natural behaviour of systems and eventually to be able in predicting such behaviour once the system's parameters and relevant conditions are known and can be specified. The integration of accumulated theoretical as well as experimental knowledge allows us to present such a unifying theory underlying the equivalence between habit and habitat in population growth. While the focus of the initial development was derived from microorganisms, the theory is extended to other population types too. The biological interpretation of ‘inertia’ or ‘habit’-based processes is provided as a consequence of this theory, and its relationship to the population ‘resource utilization’ available in the ‘habitat’ is derived. This paper focuses on the link between the ‘resource utilization’, which is related to the ‘habitat’, and ‘biological inertia’, which is related to population ‘habit’. This link extends the context of population growth and predictive modelling of microorganisms.